Photographic etch-bleach baths

ABSTRACT

A PROCESS FOR GELATIN RELIEF IMAGES IS DESCRIBED, COMPRISING BATHING THE EXPOSED AND DEVELOPED SILVER HALIDE EMULSION IN AN ETCH BLEACH BATH. THE ETCH BLEACH BATH CONTAINS HYDROGEN PEROXIDE, CUPRIC IONS, HALIDE IONS AND AT LEAST 50 GRAMS PER LITER OF UREA.

United States Patent U.S. Cl. 96-36 3 Claims ABSTRACT OF THE DISCLOSUREA process for gelatin relief images is described, comprising bathing theexposed and developed silver halide emulsion in an etch bleach bath, Theetch bleach bath contains hydrogen peroxide, cupric ions, halide ionsand at least 50 grams per liter of urea.

This invention relates to photography and particularly to a method offroming photographic relief images by the so called etch-bleach process.

It is known that gelatin relief images can be formed from gelatin layerscontaining a developed silver image by treating these layers withhydrogen peroxide and an activating compound. The silver is oxidised toa silver salt and the associated elatin is degraded so that it may bewashed away. This process is commonly called the etchbleach process.

The etch-bleach process has been used for the formation of relief imageswhich are dyed for colour photographic processes. The process iscommonly used on developed but not fixed image bearing silver halideemulsion layers to remove the silver so that the remaining emulsion canbe fogged and developed to form a reversal image. This process isparticularly useful in the graphic arts field.

For many purposes the amount of gelatin removed by washing the gelatinlayer after etch-bleach treatment is insufficient for subsequent use andit is necessary to augment the washing action with careful swabbing withcotton wool or a soft cloth to remove degraded gelatin adhering to thesupport. This latter step is both time consuming and laborious.

In recent years there has been a tendency for the manufacturers of thephotographic materials used in the graphic arts field, such as lith typefilms, to increase the hardness of the gelatino-silver halide emlsionlayers. This increased hardness improves the general handling facilityof the materials allowing them to be processed at higher temperaturesand improves their abrasion resistance. However, these materials arealso frequently used in the etchbleach process to provide reversedimages and the increased hardness reduces their ability to respond toknown etch-bleach baths.

It is an object of this invention to provide a novel etch-bleach bathwhich will remove silver images and adjacent gelatin from hardenedphotographic layers containing a silver image.

It is another object of this invention to provide an improved processfor formin gelatin relief images.

It is a still further object of this invention to provide etch-bleachbaths containing gelatin softening agents. It is likewise an object ofthis invention to provide an etchbleach process using a single bath andavoiding subsequent washing.

These and further objects and advantages of this invention have beenachieved by the discovery that the addition of urea to a hydrogenperoxide etch-bleach bath results in rapid bleaching of the silver anddegradation of the associated gelatin with reduced adherence to thetreated layer.

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When the etch-bleach baths of my invention are applied to photographiclayer by means of a spray, complete removal of the degraded gelatinformed by the action of the bath takes place. Immersion of aphotographic layer into the bath without agitation requires a subsequentspray-wash with warm water to bring about complete removal of thedegraded gelatin. In neither case is any swabbing or similar actionrequired and the whole process may be carried out in automatic apparatuswithout supervision.

In the preferred embodiments of my invention the etchbleach bathcontains cupric and halide ions together with hydrogen peroxide andurea. The mixed bath rapidly loses its activity so that the hydrogenperoxide is normally added as an aqueous solution to the otherconstituents immediately before use.

EXAMPLE 1 Samples of a high contrast silver halide emulsion were exposedto a positive dot image and a positive line image and developed for highcontrast silver halide emulsions supplied by Eastman Kodak Company inKodalith Super Developer for 2% minutes at 20 C. the high contrastsilver halide emulsion is a predominantly silver chloride, lith typeemulsion as described in Yule et al. US. Pat. No. 2,691,586 andMacWilliam US. Pat. No. 2,691,- 586 and carried by a biaxially orientedpolyethylene terephthalate support. The developed film samples wereimmersed for 30 seconds in a stop bath contatining 5 percent by weightof acetic acid.

The samples were then immersed in either bath A, an etch bleach bath ofknown type, or bath B an etch-bleach bath according to the inventionuntil the silver image was completely bleached. The samples were thenrinsed.

Etch-bleach bath A:

Copper sulphate, pentahydrate gm. Citric acid, monohydrate-lSO cm.Potassium bromide7.5 gm. Waterto 1 litre pH-0.91

Etch-bleach bath B:

Cupric chloride, dihydrate-10 gm. Citric acid, monohydrate gm. Urea-150gm. Waterto 1 litre pHl.50

In use each bath is mixed with an equal quantity of 10 volume hydrogenperoxide solution (3 percent by weight H 0 The resultant pH increased ineach case to 1.11 for bath A and 150 for bath B.

It was found that the time for complete removal of silver in the bath Awas 2 minutes whereas the time for bath B was only 1 /2 minutes.

After rinsing for 15 seconds in cold water to remove any adheringgelatin (in the case of samples bleached in bath A some swabbing withcotton wool was also required), the materials were exposed to light from100 watt lamp on both sides to fog the remaining silver halide anddeveloper in the developer for high contrast emulsions described aboveuntil the image was completely blackened. Finally the samples wererinsed in the stop bath and washed in running water.

The dot and line quality were particularly well retained in the samplesbleached in bath B.

EXAMPLE 2 The procedure of Example 1 was repeated using the etch-bleachbaths A and B which had been left unused in open dishes for 12, 24 and48 hours respectively. The speed of bleaching was noted in each case.

BLEACHING TIMES IN MINUTES 12 24 48 Solution age Fresh hours hours hoursBath A 2 3 3% 8 Bath B 1 /5 2 2% 6 It will be seen that the bleachingtime in each case was less using the bath B according to my invention.The long times at 48 hours were due to extensive decomposition of thehydrogen peroxide and could be shortened by the addition of furtherperoxide.

EXAMPLE 3 The procedure of Example 1 was repeated using etchbleach bathsA and B which had been left partially used in open dishes for 12 and 24hours respectively. The speed of bleaching was noted in each case.

BLEAGHING TIME IN MINUTES 12 Partially used bath. hours hours Bath A 4 8Bath 13 3 4 4 ticular reference to preferred embodiments thereof, but itwill be understood that variations and modifications can be effectedwithin the spirit and scope of the invention as described hereinaboveand as defined in the appended claims.

I claim:

1. A process for forming gelatin relief images comprising bathing asupported layer of gelatin containing a silver image obtained fromexposure and development of a light sensitive silver halide emulsion inan etch bleach bath containing hydrogen peroxide, cupric ions, halideions and at least grams per liter urea.

2. A process for'forming gelatin relief images according to claim 7 inwhich the etch bleach bath contains hydrogen peroxide, cupric chlorideand between 50 grams and 250 grams per liter of urea.

3. A process for forming gelatin relief images comprising bathing asupported layer of gelatin containing a silver image obtained fromexposure and development of a light sensitive silver halide emulsion inan etch bleach bath containing 1% percent by weight hydrogen peroxide,10 grams per liter cupric chloride, grams per liter citric acid and 150grams per liter urea.

References Cited UNITED STATES PATENTS 2,494,068 1/ 1950 Speck 96--60NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant ExaminerU.S. Cl. X.R. 9660

